Typechecking error not detected with prop and list prop?

[FissoreD]

func mk-rule prop, list prop -> prop.
mk-rule P R (P :- !, R).

I suppose this rule is not typecheckable.
Why the typechecker is happy about it?
The correct version should be P :- [! | R]

[gares]

I think the type checker considers prop = list prop because the interpreter considers lists of prop as iterated conjunctions. eg [p,q] => r works, as well as p :- [q, r] which is handy. So ! , [true] is also ok.

Does it fail at runtime?